Distribution by subsite and sector of 948 colorectal cancers diagnosed in Kansas in 1982 was analyzed in respect to sex and age in a population-based study. Regression analysis of percentage versus age showed decreasing left, increasing right, and unchanged transverse colon occurrence of cancer for both sexes. However, this was statistically significant only for women; left, -0.7066% per year (P = 0.0088) and right +0.6023% per year (P = 0.0012). Regression for seven subsites showed significant changes only for women; with rectosigmoid and sigmoid decreasing and cecum and ascending colon increasing. Similar results were obtained in analysis of the 5822 cases available in the Kansas cancer registry for the years 1978 to 1982. These findings have important implications for screening and diagnosis of colorectal cancer in the elderly, particularly women, and also provide a useful clue in the investigation of colorectal carcinogenesis.